The influence of selected acoustic cues on the perception of /l/ and /w/
Carol Espy-Wilson · The Journal of the Acoustical Society of America · 1989
In a semivowel recognition system developed by Espy-Wilson [Mass. Inst. Technol. Res. Lab. Electron. Tech. Rep. No. 531 (1987)], the sounds /l/ and /w/ were frequently confused, especially when they occurred intervocalically. In this study, the perceptual importance of some of the cues used in the recognition system, as well as some others which appear to be salient, were investigated. An [ala]-[awa] continuum was synthesized. The starting point was an easily identifiable [ala] stimulus. Three factors were varied orthogonally to shift the percept towards [awa]: (1) the rate of change in the formant transitions between the semivowel and following vowel, (2) the rate of change in the amplitudes of F3, F4, and F5 between the semivowel and following vowel, and (3) the spectral shape of the semivowel (coronal or labial). Preliminary results of an identification test show that spectral shape and the rate of change of the formant transitions are important cues, whereas the rate of change in the amplitudes of F3, F4, and F5 appears to have a negligible effect on listeners' responses. For example, with formant transitions of 30 ms or less, [ala] is heard. With formant transitions greater than 40 ms, the perception moves towards [awa]. The results also show that a few listeners had difficulty hearing [awa] when the semivowel had a coronal shape, despite the rate of change in the formant transitions being biased towards /w/. These results will be discussed with respect to past and future research in speech recognition.